Generally, when producing a rubber good such as a tire, a step of adding a filling material (filler) to a rubber material (crude rubber) used as an ingredient of the rubber good is carried out first. This filling material is mixed with a reinforcement component such as carbon black or silica. However, recently in most cases silica is used for the purpose of enhancing the strength of a rubber material.
Also, in some cases a reinforcement component such as silica is added to a synthetic resin material, such as polyolefin resin including polyethylene (PE) and polypropylene (PP), polyamide resin including nylon, or polyester resin including polyethylene-telephthalate (PET).
However, silica, which is an inorganic material, does not easily bind chemically to an organic material such as a rubber material or a synthetic resin material by itself (hereinafter, both a rubber material and a synthetic resin material are simply referred to as “resin material”). For this reason, a silane coupling agent is added to the resin material along with silica. The silane coupling agent enables easy chemical binding between the silica and the resin material by providing an organic functional group to a surface of the silica.
For example, Patent Document 1 discloses a method of kneading a high polymer material such as rubber containing silica and a silane coupling agent, by means of a batch-wise kneader. Patent Document 2 discloses a heimetically closed rubber kneader provided with a dust collecting duct for attracting a material scattered in a hopper of the kneader.
Incidentally, when kneading with a silane coupling agent as described above, this kneading needs to be performed sufficiently in order to allow the silane coupling agent to react with silica reliably. Thus, when this kneading is performed by the kneaders described in Patent Document 1 and Patent Document 2. the kneading is performed for enough extra time based on the past results, in order to cause the silane coupling agent to react with silica reliably.
However, kneading by adding the silane coupling agent to the resin material might change the state of reaction of the silane coupling agent, depending on the type of resin material used, how the materials could be shifted to one side, a temperature distribution in the kneader, or the like. This leads to significant, more-than-expected fluctuation of the kneading time and kneading conditions. Therefore, in order to knead the material sufficiently to obtain a reliable reaction of the silane coupling agent, it is desirable to accurately understand how well the resin material is kneaded inside the kneader, i.e., how much the silane coupling agent is reacted.
In response to such a demand, the kneaders described in Patent Document 1 and Patent Document 2 are not designed to actually enable understanding how well the resin material is kneaded in each kneader. Therefore, when kneading with a silane coupling agent is performed using the kneaders described in Patent Document 1 and Patent Document 2, the kneading operation may end before the silane coupling agent is not yet reacted completely, which is likely to cause variations in quality of the resin material in each batch-based kneading operation due to the insufficient action of the silane coupling agent.
In this regard, what is considered is removing the resin material after the end of kneading using the above-mentioned kneaders, and then analyzing the quality of the resin material offline. In such process, however, the next batch cannot be kneaded until the results of the analysis of the current batch are available, resulting in a reduction of productivity. In addition, the kneaders of Patent Document 1 and Patent Document 2 each sometimes require a long time to knead the material. For instance, these kneaders are likely to continue an unnecessary kneading operation even after the reaction of the silane coupling agent is completed, which is inefficient and likely to lower productivity significantly.